Typical end closures for beer and beverage containers have an opening panel and an attached leverage tab for pushing the opening panel into the container to open the end. The container is typically a drawn and ironed metal can, usually constructed from a thin plate of aluminum. End closures for such containers are also typically constructed from a cutedge of thin plate of aluminum or steel, formed into a blank end, and manufactured into a finished end by a process often referred to as end conversion. These ends are formed in the process of first forming a cutedge of thin metal, forming a blank end from the cutedge, and converting the blank into an end closure which may be seamed onto a container.
These types of container ends have been used for many years, with almost all such ends in use today being the "ecology" or "stay-on-tab" ends in which the tab remains attached to the end after the opening panel is opened. Throughout the use of such ends, manufacturers have sought to save the expense of the metal by downgauging the metal of the ends and the tabs. However, because ends are used for containers with pressurized contents, the score of the opening panel must have sufficient score residual to withstand such pressure, which in turn requires that the tab have a thickness of metal to provide strength to open the panel. Further, with the more recent popular use of large-open ends, additional problems arise with regard to openability of the ends. Because of the enlarged size of the opening panel (or tear panel), more stress is placed on the tab during opening of the tear panel, constraining efforts to further downgauge the tab. Also, the score in certain regions of the large-open tear panel are more difficult to open by the tab leveraging against the tear panel. This is especially true for the region of the score which is in the 5:00 to 6:00 clock position (with the rivet and tab nose being the 12:00 position).
Yet another problem with such ends is a slack of metal in the rivet area of the center panel resulting from the end conversion process. The slack of metal makes opening of the tear panel by the tab difficult because of the loss of necessary leverage by the tab. When the tear panel is initially severed, a very small amount of slack metal in the area around the rivet is helpful to initiate separation of the scoreline. However, the existence of any greater amount of slack causes panel lift when forcing the tab against the tear panel, thereby decreasing the efficiency and leverage of the tab.
Another problem with such container ends is corrosion of the metal of the score, the area called the score residual. This corrosion, often referred to as stress corrosion, is primarily caused by moisture build-up in the score, sensitivity of the metal, and tensile stress forces in the metal of the score area. The moisture build-up is primarily caused by water remaining on the end after a washing operation performed by a filler (such as with a beer or soft drink filling operation). Also, increased humidity resulting from elevated temperatures is especially a problem when a pallet or tray of the filled containers is wrapped in plastic shrink wrap, thereby trapping the moisture on the ends. The tensile stress state of the metal is increased by elevated temperature creating increased internal pressure of the container, thereby causing tensile stress forces in the metal of the score area.
Another problem with such container ends is the restriction to the material and cost savings when seeking to make the ends from a thinner metal stock (downgauging), primarily due to the fact that the traditional geometry of such ends requires one to make the ends from a larger cutedge of metal when attempting to make the end of thinner gauge metal.
As is explained in greater detail below, the present invention reduces or eliminates these problems with ecology type ends and the problems with the large-open ends.